STRANGE SOUND - LIKE SAND IN THE DASHBOARD

About a week ago, my car's A/C started making a strange sound when I turn the steering wheel - it sounds like sand running through the dashboard. It rarely makes this sound when I am driving in a straight line.

The A/C still works fine cooling down the car, however the sound is annoying and I'm worried that running the A/C might create damage. I do not see any leaks or anything like that after the car has been parked for a while.

The reason I think it is the A/C is that when I turn it off completely, the sound disappears.

The dealership wants $100 to even diagnose the problem. Any help would be greatly appreciated.